In general, that means in the state of the art, such medium voltage vacuum circuit breakers mainly consist of a drive mechanism and electric poles. Vacuum interrupters are installed within the poles. The drive is connected to the vacuum interrupters via pushrods which actuates the mechanical movement of the switching contacts inside the vacuum interrupters. The poles provide the mechanical support to the vacuum interrupters, and are fixed to the circuit breaker structure and therewith to the gas-insulated switchgear panel.
The pole-design has to withstand the dielectric, thermal and mechanical stress during service and testing conditions.
In respect of dielectric stress the insulation parts of electric poles must provide sufficient electric creepage distance on electrically stressed paths and sufficient high electric resistivity. Furthermore the design should avoid thin gas gaps between insulating and electrically stressed parts where an accumulation of the electric field appears. The poles have to be arranged inside the switchgear in a way that sufficient electric clearance is provided between the poles and earthed parts of the switchgear and between the poles in multiphase systems.
In respect of thermal stress the insulating parts of electric poles must withstand the ambient temperature in the circuit breaker compartment and the temperature of conducting parts with which they are in contact. Mechanical and dielectrical properties of the insulating parts of the poles must not change inappropriately.
In respect of mechanical stress, the pole design and especially the mechanically supporting parts of the poles must withstand the mechanical stress during switching of the circuit breaker and the electromagnetic forces during fault current.
In general the electric poles of medium voltage circuit breakers are arranged in parallel to each other. The mechanical stress caused by electromagnetic forces on parallel poles in a switchgear which is subject to fault current is directly proportional to the square of the fault current and indirect proportional to the pole distance.
The electric field and therewith the dielectric withstand of the gas volume between parallel poles depend indirectly on the pole-distance.
Furthermore the pole distance depends on the width of the poles, the width of the interrupting units inside the poles, on the switchgear in which the circuit breaker will be installed, the drive mechanism of the circuit breaker, etc.
As a consequence different ratings and designs of switchgears require different pole distances of the circuit breakers. In general circuit breakers with different pole distances comprise different drives which are specially designed for the corresponding pole-distance.
Known constructions lead to the following disadvantages.                High variance/number of parts and subassemblies        Preproduction of subassemblies not meaningful due to low needed volume per year of each part        Long production time        High production costs        Low quantities per part and year        High effort on product design maintenance due to high number of parts and bill of materials        Outsourcing of circuit breaker subassemblies difficult        Each rating requires characteristic design        No interchangeability of parts of different circuit breakers        